We here propose to continue for five years a prospective study that seeks to determine whether smoking cigarettes with a low yield of tar and nicotine is less hazardous than smoking cigarettes with a higher yield of tar and nicotine. The current study began in 1979. By the end of our recent five-year contract in December, 1983, 95,183 people undergoing multiphasic health checkups in two Kaiser-Permanente Medical Care Program facilities filled out questionnaires detailing their past and current use of tobacco products. In the proposed five-year extension of this project, we will continue for two years to administer smoking questionnaires in this setting, eventually identifying 30,000 current cigarette smokers and 70,000 never tobacco users for further study. We will use mailed questionnaires and telephone interviews to follow at three to five year intervals the current, regular cigarette smokers to ascertain changes in their smoking habits. We will ascertain the occurrence of hospitalizations through 1988 in Kaiser-Permanente facilities for diseases associated in previous studies with cigarette smoking in current, regular cigarette smokers and never tobacco users using computer-stored discharge records validated by chart review. We will ascertain mortality through 1987 in the current, regular tobacco users and the never tobacco users using the National Death Index. In 1989, we will carry out a comprehensive analysis of the data. First, we will study the relation of cigarette yield to total mortality in the current, regular smokers to determine overall the relative risk of higher yield cigarettes. Second, we will examine the relation of yield to mortality and the incidence of hospitalization for lung cancer, other smoking-related cancers, acute myocardial infarction, other coronary heart disease, chronic obstructive pulmonary disease, and peptic ulcer disease in the current, regular cigarette smokers to determine the relative risk of higher yield cigarettes for these specific conditions. Third, we will compare total mortality, cause-specific mortality, and the incidence of hospitalization for the above diseases in smokers of very low yield cigarettes (less than 8 mg tar) with that in never tobacco users to determine the relative risk of smoking very low yield cigarettes compared with not smoking at all.